In conventional magnetic separators or filters of this type, the filter mass is constituted as a mass of discrete particles or bodies of a magnetic material such as a magnetic grade stainless wool which may be subjected to an external magnetic field sufficient in magnitude to effect magnetization to provide a large number of regions in the mass of high magnetic field gradient along the paths of travel of the filtrable fluid to attract and retain the magnetic components and also to mechanically trap non-magnetic components therewith. Typical examples of such traditional magnetic separators and methods of their operations are described, for example, in U.S. Pat. Nos. 3,477,948 to K. INOUE and 3,567,026 to H. H. KOLM.
Important considerations in designing and operating of a magnetic separator for treating filtrable fluids are, as generally applicable to other filtering and separation techniques, reliability, efficiency and long operating life of the system. Thus it is known that the throughput of filtrate through the filter mass falls off with time as a consequence of the accumulation of a filter cake or residue upon the filtering mass and that it is then necessary to back-flush the filter mass to dislodge the magnetically attracted or mechanically retained contaminants or residues from the filter mass for a subsequent filtering operation. A problem therefore lies in determining, for the purposes of efficient use of the filter mass and insuring an extended life thereof, the precise time at which the filtering operation should be terminated and the back flushing effected. This is especially the case where the filterable fluid contains magnetically susceptible components of a sub-microscopic size where a drop in capability or filtering rate of a magnetic separator cannot adequately be determined by a simple measurement of head or pressure differentials between inlet and outlet sides of the filter mass or otherwise. Differences in filtering capability affect the efficiency of successive filtering cycles and the excessively prolonged time span of its use may make the system inadequate for restoration.